Core barrel outer tubes have relatively thin walls at the American Petroleum Institute (API) standard connectors that are used to connect them together in the field. The API connectors comprise “pin”, “male” or screw connectors and “box”, “female” or socket connectors as is well-known. These API connectors are inserted into or formed in the open ends of the core barrel outer tubes. Typically, a “pin” connector is provided at one end of the core barrel outer tube and a box” connector at the other end of the core barrel outer tube. In the field, for example, on a rig floor, a pin connector is joined to a box connector to join two core barrel outer tubes together.
“Rig-tongs” have conventionally been used for making the connections between core barrel outer tubes. The pressure applied to the core barrel in the vicinity of the “pin” and “box” connectors by “rig-tongs” is not normally sufficient to cause serious damage to the core barrel outer tubes as they are being connected to one another. However, for reasons of safety, these “rig-tongs” are being replaced by automated equipment, in particular, automated rig-floor torque wrenches. When making connections using automated rig-floor torque wrenches, the core barrel outer tubes may be damaged or destroyed due to one or more of the pressure applied to the thin walls during the connection process; the small distance between automated tongs that causes the tongs to grip directly over the outer tube connection where the wall thickness is the thinnest; and excessive pressure exerted by jaws of such automated tongs to achieve the required torque for a satisfactory connection between the tubes.
A conventional way of overcoming the problems created by automated equipment is to replace the entire core barrel outer tube with a stronger, thicker core barrel outer tube. This has the disadvantage of increasing the cost of each core barrel outer tube due to the increased raw material needed to make the stronger, thicker core barrel outer tube, as each core barrel out tube has a typical length of between 8 m and 10 m (between approximately 26 ft and 32 ft).